1. Field of the Invention
This invention relates to pumps and particularly to positive displacement pumps for high pressure applications.
2. Description of the Prior Art
High pressure pumps are used in water blasting systems to blast away scale, deck paint, rust or contaminants with a high pressure stream of water. Such systems have applications in oil refineries, chemical plants, oil field operations, offshore operations, and marine industries. Pumps capable of producing pressures up to 50,000 psi have been used with both water systems and water-and-sand-injection systems. These pressurizing pumps are designed to deliver high pressure water or other fluid and are usually based on positive displacement pistons or rubber/diaphragm/hydraulic systems. They may discharge the water or fluid into a common manifold to which are connected flexible hoses or rigid tubings which in turn have nozzles or lances connected to them. The pumps can be mobile or permanently mounted.
U.S. Pat. No. 3,870,439 discloses a fluid end or head for a high pressure pump which is designed specifically for high pressure cleaning service. It has been made with stainless steel parts which afford corrosion resistance and relatively long service life and it has been provided with a modular design which permits quick and easy maintenance. The fluid end can be overhauled in less than two hours and the suction and discharge valves are contained in a clamped valve seat that is easily removable for maintenance. The fluid end also has self-adjusting plunger packing contained inside a removeable cartridge for quick removal, inspection or replacement. Peak pressures developed by the pump plunger, particularly during cavitation, are transmitted to the valve seat unit and to the pump plunger packing rather than to the much more expensive pump manifold.
Despite the advantages and success of the pump fluid end of U.S. Pat. No. 3,870,439, failures have occurred while a pump with such an end operated above pressures of 12,500 p.s.i. High cyclic stresses at high pressures have caused such pump fluid ends to fail due to metal fatigue at a variety of locations within the fluid end. Typical fatigue points include: the packing-cartridge-fluid-cylinder interface; the recess for a front bushing; a recess within the fluid cylinder for the packing spring; recess for the suction valve spring; and a recess for a discharge valve flow.